The proposed research will investigate the cellular mechanisms involved in the loss and renewal of LH receptors in the plasma membrane of ovine luteal cells. It appears that LH binds to specific receptors and activates adenylate cyclase. The LH-receptor complex is then internalized and the LH is degraded. It will be determined if the receptor is also degraded or if it is recycled through the Golgi apparatus and re-inserted into the plasma membrane. It will also be determined whether exocytosis of protein containing secretory granules is involved in renewal of LH receptors. The kinetics of loss and renewal of receptors for LH will be studied in cultured ovine luteal cells using 125I-hCG to label the receptor. The process of activation of adenylate cyclase by hormone-receptor complexes will also be studied. Pretreatment of luteal tissue with prostaglandins F2 alpha inhibits the ability of LH to stimulate the activity of this enzyme and may be a useful tool to study the mechanisms involved in activation of this enzyme. A second area of research is to ascertain how LH stimulates progesterone secretion. Progesterone may be sequestered into the protein containing secretory granules and released via exocytosis. The compartmentalization of steroidogenesis and steroid secretion will be studied using a number of techniques.